Combination photographic and magnetic sound mechanism



May 31, 1955 J. L. PETTUS 2,709,596

COMBINATION PHOTOGRAPHIC AND MAGNETIC SQUND MECHANISM Filed OC'L. 29. 1949 IN V EN TOR. $475! 57705 COMBINATION PHOTOGRAPHIC AND MAGNETIC SOUND MECHANISM James L. Pettus, Encino, Calif., assignor to Radio Corporation of America, a corporation of Delaware Application October 29, 1949, Serial No. 124,313

3 Claims. (Cl. 274-4) This invention relates to sound recording, and particularly to a combination photographic and magnetic film recorder in which a minimum change is required to adapt the recorder to either type of recording.

With the advent of magnetic recording on film, similar in size and form to photographic motion picture film, there has been a tendency to utilize the usual type of photographic recorder mechanism, particularly the film drive or advancing mechanism, which has been developed and improved over many years to provide a particularly constant and uniform film motion at the light translation or recording point. The film has generally been advanced by a sprocket or sprockets around a drum having a flywheel or other inertia means, together with damped resilient filter rollers in the film loops between the drum and sprocket. The film, therefore, had excellent speed uniformity as it passed around the drum, and the sound modulated light for recording, or the constant light beam for reproduction, was impressed on the film while on the drum. However, magnetic recording, reproducing, and erase heads must physically contact the magnetic film, so in past combination photographic and magnetic recorders, the heads have been placed as near as possible to the drum, but there was always a short length of film between the drum and the head.

The present invention permits the magnetic head to be in contact with the film while on the constant speed drum, which provides the magnetic film with the same uniformity of speed at the recording point as photographic film. This is accomplished by slightly tapering the drum outwardly toward an edge guiding flange and providing the drum with an annular insert of soft material such as rubher. This construction permits better traction between the drum and film, and because magnetic film varies slightly in thickness, the head will not rise and fall with these variations to vary the head and film contact, since they will be accommodated by the resiliency of the rubber. However, should the head have a rise and fall for any reason, the rubber will provide a cushion for such movements.

The principal object of the invention, therefore, is to facilitate the recording of sound, either photographically or magnetically.

Another object of the invention is to provide an improved combination photographic and magnetic sound recording and reproducing mechanism.

A further object of the invention is to provide an improved magnetic sound film drive and head combination.

A still further object of the invention is to provide an improved system of obtaining uniform film motion at a magnetic translation point.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description, read in conjunction with the accompanying drawings, forming a part hereof, in which:

nited States Patent 2,709,596 Patented May 31, 1955 Fig. 1 is a diagrammatic view of the essential elements of a combination photographic and magnetic film recording mechanism, and

Fig. 2 is a cross-sectional view of the film drum and head taken along the line 2--2 of Fig. 1.

Referring now to the drawings, a film 5 which may be either photographic or magnetic and either thirty-five millimeter or sixteen millimeter, is shown being held on one side of sprocket 6 by a pair of pad rollers 7, and on the other side of the sprocket by a pair of pad rollers 8. The film 5 is advanced in the direction of the arrow, and passes around a filter roller 10 mounted on an arm 11, pivoted at 12, and held in tension against the film by a spring 13. The film then passes around a drum 15, mounted on a shaft 16, which preferably has a flywheel or similar inertia device (not shown) also mounted thereon. The remaining path of the film 5 between drum 15 and sprocket 6 is around filter roller 18, mounted on the end of arm 19, pivoted at 20. The other end of arm 19 has a spring 21 attached thereto to resiliently hold the roller 18 in the film loop, the arm also having a damping dashpot 22 or similar type of damping device connected thereto. This is a standard form of tight loop film drive, which provides a uniform and constant motion to the film as it passes around the drum 15.

To record a photographic sound record, sound modulated light is projected by an optical unit 24 to a photographic film 5 at the translation point 25 in the usual man ner well-known in the art, the film having uniform motion as it passes around the drum 15. To record or reproduce sound on or from a magnetic film 5, a magnetic head 27, mounted on an arm 23, pivoted at 29, is brought into contact with the film by gravity or under spring tension. The head 27 may be held out of contact with the film in the position shown by the dotted lines by a latch 31, pivoted at 32, and adapted to hook a pin 33.

To provide the desired traction between film 5 and drum 15, proper edge guiding, and the required contact between the head gap and the film, the construction shown in Fig. 2 is employed. This permits the head to contact the magnetic film while on the drum where the film speed is uniform. in Fig. 2, the surface of the drum which the film 5 contacts has a slight increasing taper toward an edge guiding flange 35, which causes the film to urge itself toward the flange at all times. Furthermore, an annular groove is formed in the drum surface in which is inserted and fastened in any suitable manner a rubber ring or tire 36. The surface of the ring is flush with the surface of the drum, and its width is greater than the width of the head 27, so that as the thickness of the film varies, the resiliency of the ring will let the surface of the film in contact with the rubber rise and fall and prevent a similar action of the head, since the other film surface will be maintained concentric with the axis of the drum. The head serves as a pressure roller or shoe to some extent, and the rubber maintains a high traction of the film with the drum to permit the drum to reach the linear speed of the film in a short time after the recorder is started. In the event the head should rise and fall, the rubber provides the necessary cushioning effect.

By the above construction, the recorder may be quickly changed from a photographic one to a magnetic one simply by releasing the head 27 from its latch 31 and lowering it onto the fiim. The recorder is always in readiness to record photographic film. Magnetic film may also be reproduced in the same manner, while in each instance, the film at the translation point always has a uniform speed. Furthermore, if a photographic film has a strip layer of magnetic particles thereon under the head, both magnetic and photographic records can be recorded simultaneously.

I claim:

1. A film drive-system adapted to advance either magnetic or photographic film comprising a sprocket for advancing a film, a drum rotatable by film pulled thereover by said sprocket, the film between said sprocket and drum being in tight loops, mechanical film motion filter means in said film loops between said drum and sprocket, said filter means providing said film with a substantially uniform motion around said drum, a magnetic head, an arm on one end of which said head is mounted, and means for pivoting said arm above said drum, said head thereby contacting said film when on said drum, the weight of said magnetic head on said film while in contact With said drum causing said head to serve as a pressure shoe to aid said mechanical film motion filter to pro- L vide a uniform motion of said film on said drum.

2. A film drivesystem adapted to advance either magnetic or photographic film in accordance with claim 1, in which said drum is provided with a resilient tire inserted in the central portion of the surface thereof for cushioning the film while on said drum and at the point of contact of said film with said head and providing traction between the film and drum as said film rotates said drum.

3. A film drive system adapted to advance either magnetic or photographic film in accordance with claim 1, in which said drum as a single flange at one end thereof and is provided with a slight taper, the larger diameter of said taper being adjacent said flange.

References Cited in the file of this patent UNITED STATES PATENTS 704,203 Moorehouse .luly 8, 1902 1,878,577 Cawley Sept. 20, 1932 1,980,978 Anderson et al Nov. 20, 1934 2,019,147 Loomis et al. Oct. 29, 1935 2,082,456 Liedtke June 1, 1937 2,153,529 Rouse Apr. 4, 1939 2,166,079 Ricchiardi July 11, 1939 2,338,414 De Sart etal Jan. 4, 1944 2,442,400 Collins June 1, 1948 2,479,868 Rossman et a1 Aug. 23, 1949 2,535,480 Begun Dec. 26, 1950 2,637,785 Charlin May 5, 1953 FOREIGN PATENTS 582,180 Germany Feb. 24, 1931 69,273 Norway May 28, 1945 OTHER REFERENCES Publication, 35 Magnetic Recording System by Earl Masterson, vol. 51., No. 5 of the Journal of the Society of Motion Picture Engineers, pages 481488, published November 1948, and also presented May 18, 1948, at the SMPE Convention in Santa Monica. (Copy available in Patent Ofiice Division 16, Class 179-1002.) 

